Amphibious vehicle

ABSTRACT

A sit-stride amphibious vehicle configuration which supports a high performance envelope both on land as well as in water. The vehicle has a planing hull and four retractable wheels. Handlebars provide for directional control in both modes of operation. Each road wheel is retractable by pivoting through at least 45° so as to maximize ground clearance when in the land mode of operation and to minimize drag at substantial lean angles when in the marine mode of operation. While a jet drive may remain directly connected to the engine at all times, the drive wheels are only connected during land mode via a speed-change transmission. The entire power train is supported by a frame that is separable from the hull which in turn has a detachable top deck portion, whereby such configuration simplifies the construction, repair and servicing of the vehicle.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from Great Britain Application SerialNos. 0423463.9, 0423470.4, 0423474.6, 0423483.7 and 0423517.2, all filedOct. 22, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to an amphibious vehicle and inparticular, to a sit-astride amphibious vehicle having all-terrainvehicle (ATV) capability on land.

Amphibious vehicles are now well known in the art. However, the presentapplicant has identified a need for an amphibious vehicle having ATVcapability on land and which performs as a high speed personalwatercraft on water. A number of prior art proposals have proceeded toprototype. However, such vehicles have opted to either optimiseoperation in the marine mode or, alternatively, operation in the landmode. The result is an amphibious vehicle having poor performance in onemode of operation or the other.

Sit astride amphibious vehicles have previously been described such asin U.S. Pat. No. 5,690,046 to Grzech. Grzech teaches an amphibioustricycle. The problem identified by the inventor in this document, wasto provide his personal watercraft (PWC) with limited on land capabilityin order that it was at least partially mobile when going ashore. GRZECHis limited in that it is only suitable for travel on well made up roadswhen operating in a land mode. This is because the vehicle has onlythree wheels and these are connected to the remainder of the vehicle bya suspension arrangement which is adapted to cope only with smooth roadsurfaces and does not have the suspension travel suitable for off-roaduse of the vehicle. Also, GRZECH needs a large heat exchanger whichprotrudes through the keel of the vehicle to provide the very necessarycooling required to cool the highly overpowered marine combustionengine. This dictates against off-road land use since the heat exchangercould easily be damaged in such a use. GRZECH has opted for a singlesteerable front wheel since this is easiest to provide in an adaptationof a personal watercraft.

Accordingly, there exists the need for an all terrain high speedamphibian vehicle, more particularly, having at least four retractablewheel assemblies.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides an amphibious vehiclecomprising:

a sit-astride seat,

a planing hull,

at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location, two of the wheelsbeing front steerable wheels, which are, at least in the land mode ofthe vehicle, connected to handlebars which can be operated by a driverto steer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and

marine propulsion means to propel the vehicle on water.

GRZECH only seeks to provide a PWC with a limited on-land function; hehas taken an existing PWC and adapted it with few changes. GRZECHteaches that the engine can be connected to the driven wheels through atransmission with one fixed gear ratio.

In a second aspect the present invention provides an amphibious vehiclecomprising:

a sit-astride seat

a planing hull,

at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location, at least two of thewheels being front steerable wheels, which are, at least in the landmode of the vehicle, connected to handlebars which can be operated by adriver to steer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and

marine propulsion means to propel the vehicle on water.

GRZECH in adapting a PWC has sought to keep the overall dimensions ofthe vehicle within those of an existing PWC; thus he has chosen rearwheels on a trailing arm suspension with a track width less than thehull beam and also a single retractable front wheel.

In a third aspect the present invention provides an amphibious vehiclecomprising:

a sit-astride seat,

a planing hull,

at least four wheels, all of which are movable between an extended landmode location and a retracted water mode location, each being pivotedabout an axis running fore and aft along the vehicle when moved betweenthe land mode and the water mode locations thereof, two of the wheelsbeing front steerable wheels, which are, at least in the land mode ofthe vehicle, connected to handlebars which can be operated by a driverto steer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and

marine propulsion means to propel the vehicle on water.

In a fourth aspect the present invention provides an amphibious vehiclecomprising:

a sit-astride seat,

a planing hull,

at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location, two of the wheelsbeing front steerable wheels, which are, at least in the land mode ofthe vehicle, connected to handlebars which can be operated by a driverto steer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and

marine propulsion means to propel the vehicle on water, wherein:

the planing hull is formed as a single component and the vehicle has oneor more deck components all joined to the hull component along a joinline which extends around an entire periphery of the vehicle at a levelabove a water line of the vehicle in water; and

the or at least one of the deck components forms a majority of anupwardly facing surface of the vehicle and is demountable to allowaccess to the engine located there beneath.

In a fifth aspect the present invention provides an amphibious vehiclecomprising:

a sit-astride seat,

a planing hull,

at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location, two of the wheelsbeing front steerable wheels of the vehicle, which are, at least in theland mode of the vehicle, connected to handlebars which can be operatedby a driver to steer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone wheel to drive the wheel, and

marine propulsion means to propel the vehicle on water, wherein:

the engine is mounted on a frame releasably connected to the hull, thevehicle also comprising a transmission connecting the engine to thedriven wheel(s), at least part of the transmission also being mounted onthe frame.

In a sixth aspect the present invention provides an amphibious vehiclecomprising:

a sit-astride seat,

a vehicle body having a planing hull,

at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location, two of the wheelsbeing steerable wheels, which are, at least in the land mode of thevehicle, connected to handlebars which can be operated by a driver tosteer the vehicle,

an engine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and

marine propulsion means to propel the vehicle on water, wherein:

the vehicle body defines a pair of footwell areas spaced apart on bothsides of the sit-astride seat with the vehicle body having sill portionspositioned laterally outside the footwell areas.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of preferredembodiments which, taken in conjunction with the accompanying drawings,illustrate by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view from above of an amphibious vehicleaccording to the present invention;

FIG. 2 is a perspective view from below of the amphibious vehicle ofFIG. 1;

FIG. 3 is a top plan view of the amphibious vehicle of FIG. 1;

FIG. 4 is a bottom plan view of the amphibious vehicle of FIG. 1;

FIG. 5 is a side elevation view of the amphibious vehicle of FIG. 1;

FIG. 6 is a front elevation view of the amphibious vehicle according toFIG. 1;

FIG. 7 is a rear end elevation view of the amphibious vehicle of FIG. 1;

FIG. 8 is a view of the vehicle of FIG. 1 in which the top surface ofthe vehicle has been made transparent;

FIG. 9 is a perspective view of a steering and suspension assembly ofthe vehicle;

FIG. 10 is a front elevation view of the steering and suspensionassembly of FIG. 9, with the wheels in their lowered land mode operationlocation;

FIG. 11 is the same front elevation view as FIG. 10, but with the wheelsraised in marine mode operation;

FIGS. 12-18 correspond to the views shown in FIGS. 1-7 save that theviews shown in FIGS. 13 to 18 show the amphibious vehicle with its wheelassemblies retracted for use in marine mode

FIG. 19 is a perspective view of a rolling chassis of the vehicle; and

FIG. 20 is a diagrammatic view of a transmission of the vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, there can be seen an amphibious vehicle10 having a forward bow end 12 and a rear stem end 14.

The vehicle 10 has four road wheels 50,51,52,53 which are connected tothe remainder of the vehicle by a wheel suspension system which includesa wheel retraction mechanism for moving the wheels 50,51,52,53 between alowered state for road use and a raised state for marine use. The frontwheels 50 and 53 are steerable and handlebars 54 enable steering ofthese wheels. The rear wheels 51,52 are driven to propel the vehicle onland. A jet drive unit 55 (see FIG. 2) provides propulsion in marineuse.

The structure of the amphibious vehicle 10 comprises an upper decksection 30 and a lower hull section 40. The upper deck structure 30 issealed to the lower hull section 40 around a peripheral planar edgewhich is above the water line when the amphibious vehicle 10 isdisplaced in water—(as can best be seen in FIG. 5 and FIG. 8). Thecomplete upper deck section 30 is detachable from the lower hull section40 as a single unit; this permits ease of access to internal componentsof vehicle for servicing, etc.

Air inlet openings 31 provide an entry for cooling air (e.g.fan-assisted) for use by the cooling systems of the amphibious vehicle10. Air entrained via inlets 31 is eventually exhausted via outlets 32.Between air inlet 31 and air outlet 32, a dorade system is installed toprevent the ingress of water. The dorade system facilitates righting ofthe vehicle on water by use of a labyrinthine air inlet passage systemto prevent the ingress of water should the amphibious vehicle 10 beinverted in use in the marine mode. Sit-astride seats 33 and 34 areprovided for a driver and a passenger of the amphibious vehicle 10. Afootwell area 35 is provided either side of the sit-astride seats 33,34, each shrouded by bodywork positioned laterally outside of thefootwell area 35 to provide protection. These footwell areas 35 may beprovided with means to bail automatically any water shipped in use ofthe amphibious vehicle 10.

Front and rear wheel arches 36, 37 are provided on either side of theamphibious vehicle 10 so as to contain a retractable wheel assemblywhich is retracted when the amphibious vehicle 10 is operating in themarine mode. An instrument panel 38 is provided ahead of the steeringcontrols to convey relevant parameters of the amphibious vehicle 10 tothe driver. Additionally, rear view mirrors (not shown) may be providedas a visual aid to the driver. Furthermore, navigation lights may alsobe provided within or on the upper deck structure 30 in accordance withthe local legislative requirements.

The upper deck structure 30 forms an integral part of the entirestructure of the vehicle. It is a structural component and not merelycladding. Typically it will take the form of a composite structure (e.g.glass fibres or carbon fibres set in resin) although any suitablemanufacturing method may be employed. Where localised areas of strengthare required in the upper deck structure 30, extra layers or mats offibres may be laid down during manufacture. The deck 30 will be formedwith localised reinforced areas in order to provide a complete forcetransmitting path extending around the vehicle in a complete circle in aplane orthogonal to a longitudinal axis of the vehicle, in order toprovide resistance to torsional loads on the vehicle.

Referring now to FIGS. 2 and 4 the underside of the hull can be seenextending from the front bow section 12 to the rear stem section 14.Starting from the planar interface with the upper deck section 30, thereis a relatively shallow section 41 extending around a periphery of theamphibious vehicle 30 and in this section there are provided front andrear wheel arches 42, 43. These areas of the hull provide stability whenthe amphibious vehicle 10 is operated at high speed in marine modebecause they provide enclosed volumes spaced laterally from the centreline of the amphibious vehicle 10. As such, when cornering sharply, forexample, an increase in righting force is experienced as the angle oflean increases. The bodywork lateral of the footwell areas could beprovided with buoyancy inserts which would provide righting forcesspaced from the vehicle centre line when the vehicle comers on water.

Cutouts are provided in the hull on either side of the centre line ofthe vehicle in the region of the front and rear wheel arches 42, 43 toprovide slots through which the retractable wheel assemblies can beprotracted and retracted. Suitably profiled covers 44, 45 are providedas part of the wheel assemblies so as to reconstruct the lines of thehull when the wheel assemblies are retracted for use in marine mode.

A lower V section 46 depends from the mid section 41 and is providedwith a keel section running from the bow 12 of the amphibious vehicle toapproximately halfway along the length of the vehicle. At this point,the keel splits to incorporate a water intake area 49 for a jet drivemarine propulsion unit of the amphibious vehicle 10. The design of thehull 40 is critical in determining the performance achieved when theamphibious vehicle 10 is operated in the marine mode.

The present applicants have spent considerable time and effort in thedesign of the hull 40 which has resulted in a rather surprising shape inthat usually expected for a planing water craft. The dead rise angle ofthe hull is substantially 20.7 degrees along substantially its entirelength. This compares with traditional planing hulls which start at thebow section with a very steep dead rise angle and these dead rise anglesbecome more shallow along the length of the hull towards the stem,typically ending at 5 degrees or less of dead rise angle.

Since the seating of the vehicle is arranged longitudinally along thevehicle, the vehicle is narrower than a passenger car. Aligning theengine longitudinally along the vehicle gives a body shape which isnarrow in beam and deep. Rather than adopting the flat planing hullcommon in the prior art, the applicant has adopted a greater dead riseangle for the agile marine handling this provides, accepting that thisgives a need for a suspension with a lot of travel to give adequateground clearance on land. Large wheels also enable off-road usage,although they give problems of packaging. Whereas before vehicles suchas that of GRZECH strove to keep the track width of the wheels withinthe beam of the vehicle, the applicant has realised that better landmode operation can be achieved if the track width of the vehicle isgreater than the beam of the hull. The approach adopted by the applicantdoes mean that wheels must be retracted through a large angle in orderto be clear of the vehicle waterline in marine use, but the strategydoes provide for a vehicle capable both on land and on water.

The hull 40 is additionally provided with hydrodynamic aids in the formof strakes 47, 48 and the profiled suspension arm covers 44, 45previously referred to. Even with the small footprint of the hull of theamphibious vehicle 10, the hull design 40 is capable of propelling theamphibious vehicle 10 up onto the plane with little difficulty in fasttime periods. Furthermore, on-water performance of the amphibiousvehicle 10 is not compromised and adequate ground clearance is availablein operating the amphibious vehicle 10 in land mode as an all terrainvehicle.

FIG. 8 illustrates location of the major internal components of theamphibious vehicle 10.

In FIG. 8 there can be seen a prime mover 60 which is a multi-cylinderinternal combustion engine. It is connected by a transmission 61 todrive the rear wheels 51,52 during land use of the vehicle and to drivethe jet drive unit 55 during marine use. As described in otherapplications of the applicant the jet drive unit is permanentlyconnected to the engine 60 to be driven thereby at all times, whilst thewheels 51 and 52 are connected to the engine 52 only in their loweredland use positions.

In FIG. 8 it can be seen that the handlebars 54 are connected by asteering column 62 to a steering mechanism 63 for steering the frontwheels 50,53 of the vehicle which is described in detail in anotherapplication of the applicant. Spring and damper assemblies 64,65,66,67are provided in-board for the wheels 50,51,52,53. Two wheel retractionhydraulic actuators (which cannot be seen in the Figure) are provided,one for the front wheels 50,53 and one for the rear wheels 51,52 toallow the wheels to be retracted from their lowered positions shown inFIG. 8 to their raised positions. These hydraulic actuators will bepowered by hydraulic fluid supplies from a pump (not shown) powered bythe engine 60.

The seating in the vehicle is provided substantially above the vehiclepowertrain, with the handlebars located roughly halfway along the lengthof the vehicle, this comparing with traditional PWC designs which locatethe handlebars roughly two thirds along the length of the vehicle(measured from the back). This gives a good weight distribution for bothmarine and land use.

The powertrain components illustrated in FIG. 8, i.e. the engine 60, thetransmission 61 are built up on a frame platform which is then connectedto the hull; this gives considerable advantage for ease of manufacture.Indeed it is envisaged that a chassis could be constructed with a framesupporting all of the wheel suspension components, the wheel steeringmechanism, the wheel retraction mechanism, the engine 60 and thetransmission 61. This would considerably aid construction and repair.This is illustrated in FIG. 19 where a rolling chassis 300 of thevehicle can be seen stripped of the surrounding hull and deck sections.In the Figure there can be seen the engine, the transmission 61 as wellas the suspension assemblies for the front and rear wheels and radiators70, 302 of the cooling system of the vehicle, all mounted to a commonsupporting structure 303.

The radiator 70 can also be seen in FIG. 8 located at the front of thevehicle which will cool the vehicle's engine, at least in land use. Thevehicle's engine can also be cooled by a water/water heat exchanger (notshown) in marine use, with water being drawn from beneath the vehicle tocool water used by the engine cooling system.

The transmission 61 comprises an output shaft 71 leading drive from theengine to a gearbox 72 which has two output shafts; a horizontallyextending shaft 73 taking drive to the jet drive unit 55 and avertically extending shaft 74 leading to a continuously variabletransmission arrangement, the pulleys 75,76 of which can be seen in FIG.8 and which is shown schematically in FIG. 20. As shown in FIG. 20, thecontinuously variable transmission has a vertically extending outputshaft 400 which extends downwardly to a differential 401 through whichdrive is relayed to the rear wheels 51,52. The CVT transmission 61 couldbe replaced in other embodiments by a conventional automatic gearbox ora manual gearbox.

FIGS. 9 to 11 show the front steering and suspension assemblies of thevehicle. A frame 101 has swingably mounted to it left and rightsuspensions 103 and 105 as seen from the rear of the vehicle.

Each suspension 103 and 105 comprises an upright member 107 (see FIG.10) connected to a lower suspension arm 109 and an upper wishbone 111.Wheels 50 and 53 (shown in FIG. 1) are each mounted to a hub 114, whichis rotatably carried on upright member 107.

Extending from each of the upright members 107 is a steering arm 117(see especially FIG. 9) to which is pivotally connected a track rodextension 119 at its outer end 121. The inner end of extension 119 isconnected to a track rod 123. The track rod 123 is moved transversely bymeans of link 125 which is connected to a swingable connection 127 onsteering column 129.

An actuator 141 having piston rod 143 acts on one arm of swing arm 137to pivot the arm, the outer ends of which are connected to piston rods144 of suspension dampers 145 (see FIGS. 10 and 11), which aresurrounded by coil springs 146. The base of each damper 145 is connectedat 147 to retraction arm 149 pivotally mounted at 151 to frame 101. Onretraction the suspension swings about an axis running fore and aftlongitudinally along the vehicle; a torsion tube 151 rotates and thelower suspension arm 109 rotates with it (compare FIGS. 10 and 11).

Whilst above a single internal combustion engine is used to both drivethe wheels is land mode operations and also to power the jet drive,separate engines could be provided, one for the road wheels and anotherfor the jet drive. Also the jet drive could be replaced by a propeller.

While a particular form of the present invention has been illustratedand described, it will also be apparent to those skilled in the art thatvarious modifications can be made without departing from the spirit andscope of the present invention. Accordingly, it is not intended that theinvention be limited except by the appended claims.

1. An amphibious vehicle comprising: a sit-astride seat, a planing hull,at least four wheels, each of which is movable between an extended landmode location and a retracted water mode location two of the wheelsbeing front steerable wheels, which are, at least in the land mode ofthe vehicle, connected to handlebars which can be operated by a driverto steer the vehicle, an engine which in the land mode of the vehicle isconnected to at least one of the wheels to drive the wheel, and marinepropulsion means to propel the vehicle on water.
 2. An amphibiousvehicle as claimed in claim 1, wherein: the engine drives the marinepropulsion means to propel the vehicle on water.
 3. An amphibiousvehicle as claimed in claim 1, comprising additionally: a speed changetransmission giving the vehicle in forward motion on land a plurality ofdifferent gear ratios between the engine and the driven wheel(s).
 4. Anamphibious vehicle as claimed in claim 1, wherein: all of the fourwheels are each pivoted about an axis running fore and aft along thevehicle when moved between the land mode and the water mode locationsthereof.
 5. An amphibious vehicle as claimed in claim 2, comprisingadditionally: a speed change transmission giving the vehicle in forwardmotion on land a plurality of different gear ratios between the engineand the driven wheel(s).
 6. An amphibious vehicle as claimed in claim 2,wherein: all of the four wheels are each pivoted about an axis runningfore and aft along the vehicle when moved between the land mode and thewater mode locations thereof.
 7. An amphibious vehicle as claimed inclaim 3, wherein: all of the four wheels are each pivoted about an axisrunning fore and aft along the vehicle when moved between the land modeand the water mode locations thereof.
 8. An amphibious vehicle asclaimed in claim 5, wherein: all of the four wheels are each pivotedabout an axis running fore and aft along the vehicle when moved betweenthe land mode and the water mode locations thereof.
 9. An amphibiousvehicle as claimed in claim 1, wherein: the two front steerable wheelsin land mode locations thereof are located on opposite sides of thevehicle, spaced apart transversely across the vehicle by a first trackwidth; the two other wheels of the four are not connected to thehandlebars to be steered thereby and are located at the rear of thevehicle on opposite sides of the vehicle, spaced apart transverselyacross the vehicle by a second track width greater than the first trackwidth.
 10. An amphibious vehicle as claimed in claim 1, wherein: aseparate spring and damper unit is provided for each wheel.
 11. Anamphibious vehicle as claimed in claim 1, wherein: a track rod ismounted to extend transversely across the vehicle; the track rod ismounted by mounting means which allow the track rod to be slid along theaxis thereof transversely across the vehicle by rotation of thehandlebars; the track rod is pivotally connected at one end to a firstfront wheel and is pivotally connected at a second end to a second frontwheel; and the front wheels are pivotally mounted on supportingsuspension arrangements for steering rotation under control of the trackrod.
 12. An amphibious vehicle comprising: a sit-astride seat, a planinghull, at least four wheels, all of which are movable between an extendedland mode location and a retracted water mode location, two of thewheels being front steerable wheels, which are, at least in the landmode of the vehicle, connected to handlebars which can be operated by adriver to steer the vehicle, an engine which in the land mode of thevehicle is connected to at least one of the wheels to drive the wheel, aspeed change transmission giving the vehicle in forward motion on land aplurality of different gear ratios connected between the engine and thedriven wheel(s), and a jet connected to the engine to be driven therebyto propel the vehicle on water.
 13. An amphibious vehicle as claimed inclaim 12, wherein all of the four wheels are each pivoted about an axisrunning fore and aft along the vehicle when moved between the land modeand the water mode locations thereof.
 14. An amphibious vehicle asclaimed in claim 12, wherein: the speed change transmission comprises amanually operable gearbox and a manually operable gear selection meansare provided operable by a driver of the vehicle to select one of thegear ratios.
 15. An amphibious vehicle as claimed in claim 12, wherein:the speed change transmission comprises an automatic gearbox.
 16. Anamphibious vehicle as claimed in claim 12, wherein: the speed changetransmission comprises a continuously variable transmission.
 17. Anamphibious vehicle comprising: a sit-astride seat, a planing hull, atleast four wheels, all of which are movable between an extended landmode location and a retracted water mode location, each being pivotedabout an axis running fore and aft along the vehicle when moved betweenthe land mode and the water mode locations thereof, two of the wheelsbeing front steerable wheels, which are, at least in the land mode ofthe vehicle, connected to handlebars which can be operated by a driverto steer the vehicle, an engine which in the land mode of the vehicle isconnected to at least one of the wheels to drive the wheel, and marinepropulsion means to propel the vehicle on water
 18. An amphibiousvehicle as claimed in claim 17, wherein: each road wheel is pivotedthrough 45° or more during retraction.
 19. An amphibious vehicle asclaimed in claim 17, wherein: the four wheels comprise a front pair ofwheels steerable by the handlebars and spaced apart transversely acrossthe vehicle by a first track width when in land mode and a rear pair ofwheels spaced apart transversely across the vehicle by a second trackwidth when in land mode; and the planing hull has a maximum beam widthwhich is less than both the first and second track widths.
 20. Anamphibious vehicle as claimed in claim 19, wherein: the first trackwidth is greater than the second track width.
 21. An amphibious vehicleas claimed in claim 19, wherein: a separate spring and damper assemblyis provided for each wheel.
 22. An amphibious vehicle comprising: asit-astride seat, a planing hull, at least four wheels, each of which ismovable between an extended land mode location and a retracted watermode location, two of the wheels being front steerable wheels, whichare, at least in the land mode of the vehicle, connected to handlebarswhich can be operated by a driver to steer the vehicle, an engine whichin the land mode of the vehicle is connected to at least one of thewheels to drive the wheel, and marine propulsion means to propel thevehicle on water, wherein: the planing hull is formed as a singlecomponent and the vehicle has one or more deck components all joined tothe hull component along a join line which extends around an entireperiphery of the vehicle at a level above a water line of the vehicle inwater; and the or at least one of the deck components forms a majorityof an upwardly facing surface of the vehicle and is demountable to allowaccess to the engine located there beneath.
 23. An amphibious vehicle asclaimed in claim 22, wherein: the hull and each deck component is formedof a composite of fibres set in resin and localised areas of at leastsome of the deck components are provided with fibre reinforcementadditional to the fibre reinforcement in a remainder of the component(s)to provide a greater structural strength in such areas, wherebyreinforced areas provide load paths for transmission of loading of thevehicle and the load paths extend around an entire transversely viewedperiphery of the vehicle to resist torsion loads acting to twist a frontpart of the vehicle relative to a rear part of the vehicle.
 24. Anamphibious vehicle comprising: a sit-astride seat, a planing hull, atleast four wheels, each of which is movable between an extended landmode location and a retracted water mode location, two of the wheelsbeing front steerable wheels of the vehicle, which are, at least in theland mode of the vehicle, connected to handlebars which can be operatedby a driver to steer the vehicle, an engine which in the land mode ofthe vehicle is connected to at least one wheel to drive the wheel, andmarine propulsion means to propel the vehicle on water, wherein: theengine is mounted on a frame releasably connected to the hull, thevehicle also comprising a transmission connecting the engine to thedriven wheel(s), at least part of the transmission also being mounted onthe frame.
 25. An amphibious vehicle as claimed in claim 24, wherein: asuspension system is provided for the road wheels and the suspensionsystem is also mounted on the frame.
 26. An amphibious vehicle asclaimed in claim 25, wherein a steering mechanism is connected betweenthe handlebars at the front steerable wheels and the steering mechanismis also mounted on the frame.
 27. An amphibious vehicle comprising: asit-astride seat, a vehicle body having a planing hull, at least fourwheels, each of which is movable between an extended land mode locationand a retracted water mode location, two of the wheels being steerablewheels, which are, at least in the land mode of the vehicle, connectedto handlebars which can be operated by a driver to steer the vehicle, anengine which in the land mode of the vehicle is connected to at leastone of the wheels to drive the wheel, and marine propulsion means topropel the vehicle on water, wherein: the vehicle body defines a pair offootwell areas spaced apart on both sides of the sit-astride seat withthe vehicle body having still portions positioned laterally outside thefootwell areas.
 28. An amphibious vehicle as claimed in claim 27,wherein buoyancy chambers are provided in the still portions of thevehicle.